Channel state information measurements for license-assisted access

ABSTRACT

Systems and methods relating to accurate Channel State Information (CSI) measurements for a License Assisted Secondary Cell (LA SCell) are disclosed herein. In some embodiments, a wireless device enabled to operate in a cellular communications network according to a carrier aggregation scheme using both a licensed frequency band and an unlicensed frequency band operates to determine whether a Channel State Information Reference Symbol (CSI-RS) transmission from a LA SCell of the wireless device is present in a subframe, where the LA SCell is in an unlicensed frequency band. The wireless device further operates to process a CSI-RS measurement for the LA SCell for the subframe upon determining that a CSI-RS transmission from the LA SCell is present in the subframe and refrain from processing a CSI-RS measurement for the LA SCell for the subframe upon determining that a CSI-RS transmission from the LA SCell is not present in the subframe.

RELATED APPLICATIONS

This application claims the benefit of provisional patent applicationSer. No. 62/012,616, filed Jun. 16, 2014, the disclosure of which ishereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure pertains to Channel State Information (CSI)measurements, and in particular, to CSI measurements for LicenseAssisted (LA) access.

BACKGROUND

The Third Generation Partnership Project (3GPP) initiative “LicenseAssisted Long Term Evolution (LTE)” (LA-LTE) aims to allow LTE equipmentto operate in the unlicensed 5 Gigahertz (GHz) radio spectrum. Theunlicensed 5 GHz spectrum is used as an extension to the licensedspectrum. Accordingly, devices connect in the licensed spectrum (PrimaryCell (PCell)) and use Carrier Aggregation (CA) to benefit fromadditional transmission capacity in the unlicensed spectrum (SecondaryCell (SCell)). To reduce the changes required for aggregating licensedand unlicensed spectrum, the LTE frame timing in the PCell issimultaneously repeated in the SCell.

Regulatory requirements, however, may not permit transmitting in theunlicensed spectrum without prior channel sensing. Because theunlicensed spectrum must be shared with other radios of similar ordissimilar wireless technologies, a so called Listen-Before-Talk (LBT)scheme is applied. Today, the unlicensed 5 GHz spectrum is used byequipment implementing the IEEE 802.11 Wireless Local Area Network(WLAN) standard. This standard is known under its marketing brand“Wi-Fi.”

LTE Overview

LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in thedownlink and Discrete Fourier Transform (DFT) spread OFDM in the uplink.The basic LTE downlink physical resource can thus be seen as atime-frequency grid as illustrated in FIG. 1, where each resourceelement corresponds to one OFDM subcarrier during one OFDM symbolinterval.

As illustrated in FIG. 2, in the time domain, LTE downlink transmissionsare organized into radio frames of 10 milliseconds (ms), each radioframe consisting of ten equally-sized subframes of length T_(subframe)=1ms. For normal cyclic prefix, one subframe consists of 14 OFDM symbols.The duration of each OFDM symbol is approximately 71.4 microseconds(μs).

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 ms) in the time domain and 12 contiguous subcarriers in thefrequency domain. A pair of two adjacent resource blocks in timedirection (1.0 ms) is known as a resource block pair. Resource blocksare numbered in the frequency domain, starting with 0 from one end ofthe system bandwidth.

Downlink transmissions are dynamically scheduled; that is, in eachsubframe, the base station transmits control information about to whichterminal's data is transmitted and upon which resource blocks the datais transmitted, in the current downlink subframe. This control signalingis typically transmitted in the first 1, 2, 3, or 4 OFDM symbols in eachsubframe and the number n=1, 2, 3, or 4 is known as the Control FormatIndicator (CFI). The downlink subframe also contains common referencesymbols, which are known to the receiver and used for coherentdemodulation of, e.g., the control information. A downlink system withCFI=3 OFDM symbols as control is illustrated in FIG. 3.

From LTE Release 11 onwards, the above described resource assignmentscan also be scheduled on the enhanced Physical Downlink Control Channel(EPDCCH). For LTE Release 8 to Release 10, only Physical DownlinkControl Channel (PDCCH) is available.

The reference symbols shown FIG. 3 are the Cell specific ReferenceSymbols (CRS) and are used to support multiple functions including finetime and frequency synchronization and channel estimation for certaintransmission modes.

In a cellular communications system, there is a need to measure thechannel conditions in order to know what transmission parameters to use.These parameters include, e.g., modulation type, coding rate,transmission rank, and frequency allocation. This applies to uplink aswell as downlink transmissions.

The scheduler that makes the decisions on the transmission parameters istypically located in the base station, which in LTE is referred to asthe enhanced or evolved Node B (eNB). Hence, it can measure channelproperties of the uplink directly using known reference signals that theterminals (User Equipment devices (UEs) in LTE terminology) transmit.These measurements then form a basis for the uplink scheduling decisionsthat the eNB makes, which are then sent to the UEs via a downlinkcontrol channel.

However, for the downlink, the eNB is unable to measure any channelparameters. Rather, the eNB must rely on information that the UEs cangather and subsequently send back to the eNB. This so-called ChannelState Information (CSI) is obtained in the UEs by measuring on knownreference symbols, CSI Reference Symbols (CSI-RSs), transmitted in thedownlink.

The CSI-RSs are UE specifically configured by Radio Resource Control(RRC) signaling, with a certain configured periodicity,T={5,10,20,40,80} ms (i.e., every Tth subframe). There is a possibilityto configure both Non-Zero Power (NZP) CSI-RSs and Zero Power (ZP)CSI-RSs where the ZP CSI-RS is simply an unused resource that can bematched to a NZP CSI-RS in an adjacent eNB. This will improve the Signalto Interference plus Noise Ratio (SINR) for the CSI-RS measurements inthe adjacent cell. The ZP CSI-RS can also be used as CSI InterferenceMeasurement (CSI-IM) resources as introduced in LTE Release 11 andexplained below.

In LTE, the format of the CSI reports are specified in detail and maycontain Channel Quality Information (CQI), Rank Indicator (RI), andPrecoding Matrix Indicator (PMI) (see, for example, 3GPP TechnicalSpecification (TS) 36.213 version 11.6.0). The reports can be widebandor applicable to subbands. The reports can be configured by a RRCmessage to be sent periodically or in an aperiodic manner or triggeredby a control message from the eNB to a UE. The quality and reliabilityof the CSI are crucial for the eNB in order to make the best possiblescheduling decisions for the upcoming downlink transmissions.

The LTE standard does not specify in detail how the UE should obtain andaverage these measurements from multiple time instants. For example, theUE may measure over a time frame unknown to the eNB and combine severalmeasurements in a UE-proprietary way to create the CSI values that arereported, either periodically or triggered.

In the context of LTE, the available CSI-RSs are referred to as “CSI-RSresources.” In addition, there are also “CSI-IM resources.” The latterare defined from the same set of possible physical locations in thetime/frequency grid as the CSI-RSs, but with ZP, hence ZP CSI-RS. Inother words, they are “silent” CSI-RSs. When the eNB is transmitting theshared data channel, it avoids mapping data to those resource elementsused for CSI-IM. The resource elements used for CSI-IM are intended togive a UE the possibility to measure the power of any interference fromanother transmitter than its serving node.

Each UE can be configured with one, three, or four different CSIprocesses. Each CSI process is associated with one CSI-RS and one CSI-IMwhere these CSI-RS resources have been configured to the UE by RRCsignaling and are thus periodically transmitted/occurring with aperiodicity of T and with a given subframe offset relative to the framestart. If only one CSI process is used, then it is common to let theCSI-IM reflect the interference from all other eNBs, i.e. the servingcell uses a ZP CSI-RS that overlaps with the CSI-IM, but in otheradjacent eNBs there is no ZP CSI-RS on these resources. In this way, theUE will measure the interference from adjacent cells using the CSI-IM.

If additional CSI processes are configured to the UE, then there ispossibility for the network to also configure a ZP CSI-RS in theadjacent eNB that overlaps with a CSI-IM for this CSI process for the UEin the serving eNB. In this way, the UE will also feedback accurate CSIfor the case when this adjacent cell is not transmitting. Hence,coordinated scheduling between eNBs is enabled with the use of multipleCSI processes where one CSI process feeds back CSI for the fullinterference case and the other CSI process feeds back CSI for the casewhen a (strong interfering) adjacent cell is muted. As mentioned above,up to four CSI processes can be configured to the UE, thereby enablingfeedback of four different transmission hypotheses.

PDCCH and EPDCCH

The PDCCH/EPDCCH is used to carry Downlink Control Information (DCI)such as scheduling decisions and power control commands. Morespecifically, the DCI includes:

-   -   Downlink scheduling assignments, including Physical Downlink        Shared Channel (PDSCH) resource indication, transport format,        hybrid Automatic Repeat Request (ARQ) information, and control        information related to spatial multiplexing (if applicable). A        downlink scheduling assignment also includes a command for power        control of the Physical Uplink Control Channel (PUCCH) used for        transmission of hybrid ARQ acknowledgements in response to        downlink scheduling assignments.    -   Uplink scheduling grants, including Physical Uplink Shared        Channel (PUSCH) resource indication, transport format, and        hybrid ARQ-related information. An uplink scheduling grant also        includes a command for power control of the PUSCH.    -   Power control commands for a set of terminals as a complement to        the commands included in the scheduling assignments/grants.

One PDCCH/EPDCCH carries one DCI message with one of the formats above.As multiple terminals can be scheduled simultaneously, on both downlinkand uplink, there must be a possibility to transmit multiple schedulingmessages within each subframe. Each scheduling message is transmitted onseparate PDCCH/EPDCCH resources, and consequently there are typicallymultiple simultaneous PDCCH/EPDCCH transmissions within each cell.Furthermore, to support different radio channel conditions, linkadaptation can be used, where the code rate of the PDCCH/EPDCCH isselected by adapting the resource usage for the PDCCH/EPDCCH to matchthe radio channel conditions.

Carrier Aggregation

The LTE Release 10 standard (and subsequent releases) supportsbandwidths larger than 20 Megahertz (MHz). One important requirement onLTE Release 10 is to assure backward compatibility with LTE Release 8.This should also include spectrum compatibility. That would imply thatan LTE Release 10 carrier that is wider than 20 MHz should appear as anumber of LTE carriers to an LTE Release 8 terminal. Each such carriercan be referred to as a Component Carrier (CC). In particular, for earlyLTE Release 10 deployments, it can be expected that there will be asmaller number of LTE Release 10-capable terminals compared to many LTElegacy terminals. Therefore, it is necessary to assure an efficient useof a wide carrier also for legacy terminals, i.e. that it is possible toimplement carriers where legacy terminals can be scheduled in all partsof the wideband LTE Release 10 carrier. The straightforward way toobtain this would be by means of CA. CA implies that an LTE Release 10terminal can receive multiple CCs, where the CCs have, or at least thepossibility to have, the same structure as a LTE Release 8 carrier. CAis illustrated in FIG. 4.

The number of aggregated CCs as well as the bandwidth of the individualCCs may be different for uplink and downlink. A symmetric configurationrefers to the case where the number of CCs in downlink and uplink is thesame whereas an asymmetric configuration refers to the case that thenumber of CCs is different. It is important to note that the number ofCCs configured in a cell may be different from the number of CCs seen bya terminal. A terminal may, for example, support more downlink CCs thanuplink CCs, even though the cell is configured with the same number ofuplink and downlink CCs.

Cross-Carrier Scheduling

Scheduling of a CC is done on the PDCCH or EPDCCH via downlinkassignments. Control information on the PDCCH/EPDCCH is formatted as aDCI message. In LTE Release 8, a terminal only operates with onedownlink and one uplink CC and, therefore, the association betweendownlink assignment, uplink grants, and the corresponding downlink anduplink CCs is clear. In LTE Release 10, two modes of CA need to bedistinguished. The first mode is very similar to the operation ofmultiple LTE Release 8 terminals. In particular, in the first mode, adownlink assignment or an uplink grant contained in a DCI messagetransmitted on a CC is either valid for the downlink CC itself or for anassociated (either via cell-specific or UE specific linking) uplink CC.A second mode of operation augments a DCI message with the CarrierIndicator Field (CIF). A DCI containing a downlink assignment with CIFis valid for the downlink CC indicted with CIF and a DCI containing anuplink grant with CIF is valid for the indicated uplink CC. The DCItransmitted using EPDCCH, which was introduced in LTE Release 11, canalso carry CIF which means that cross carrier scheduling is supportedalso when using EPDCCH.

WLAN

In typical deployments of a WLAN, Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA) is used. This means that the channel issensed, and only if the channel is declared as Idle, a transmission isinitiated. In case the channel is declared as Busy, the transmission isessentially deferred until the channel is found Idle. When the range ofseveral Access Points (APs) using the same frequency overlap, this meansthat all transmissions related to one AP might be deferred in case atransmission on the same frequency to or from another AP which is withinrange can be detected. Effectively, this means that if several APs arewithin range, they will have to share the channel in time, and thethroughput for the individual APs may be severely degraded. A generalillustration of the LBT mechanism is shown in FIG. 5.

Licensed Assisted Access (LAA) to Unlicensed Spectrum Using LTE

Up to now, the spectrum used by LTE is dedicated to LTE. This has theadvantage that the LTE system does not need to care about thecoexistence issue and the spectrum efficiency can be maximized. However,the spectrum allocated to LTE is limited and, therefore, cannot meet theever increasing demand for larger throughput from applications/services.Therefore, discussions are ongoing in 3GPP to initiate a new study itemon extending LTE to exploit unlicensed spectrum in addition to licensedspectrum. Unlicensed spectrum can, by definition, be simultaneously usedby multiple different technologies. Therefore, when using unlicensedspectrum, LTE would need to consider the coexistence issue with othersystems such as IEEE 802.11 (Wi-Fi). Operating LTE in the same manner inunlicensed spectrum as in licensed spectrum can seriously degrade theperformance of Wi-Fi as Wi-Fi will not transmit once it detects thechannel is occupied.

Furthermore, one way to utilize the unlicensed spectrum reliably is todefer essential control signals and channels on a licensed carrier. Thatis, as shown in FIG. 6, a UE is connected to a PCell in the licensedband and one or more SCells in the unlicensed band. In the presentdisclosure, a SCell in an unlicensed spectrum is referred to as aLicense Assisted (LA) SCell.

Periodic CSI measurements can be configured in LTE, where the UE ismeasuring the channel on CSI-RS in predefined subframes with aperiodicity T={5,10,20,40,80} ms. If the eNB detects, by using LBT, thatthe LA SCell channel is occupied at the configured subframe of a CSI-RStransmission, then the eNB may not be able to transmit the CSI-RS onthat LA SCell. In such a subframe, the UE will not measure on atransmitted CSI-RS but on a signal transmitted by the equipment or nodeoccupying the channel. This will lead to corrupted CSI estimates anddownlink throughput degradation, which is a problem. Under rareoccasions, regulations allow the eNB to transmit CSI-RS even in anoccupied subframe (less than 5% duty cycle); however, this would lead tointerference in the CSI estimation, which is a problem.

Thus, there is a need for systems and methods for obtaining accurate CSIestimates for a LA SCell.

SUMMARY

Systems and methods relating to accurate Channel State Information (CSI)measurements for a License Assisted Secondary Cell (LA SCell) aredisclosed herein. In some embodiments, a wireless device enabled tooperate in a cellular communications network according to a CarrierAggregation (CA) scheme using both a licensed frequency band and anunlicensed frequency band operates to determine whether a CSI ReferenceSymbol (CSI-RS) transmission from a LA SCell of the wireless device ispresent in a subframe, where the LA SCell is in an unlicensed frequencyband. The wireless device further operates to process a CSI-RSmeasurement for the LA SCell for the subframe upon determining that aCSI-RS transmission from the LA SCell is present in the subframe andrefrains from processing a CSI-RS measurement for the LA SCell for thesubframe upon determining that a CSI-RS transmission from the LA SCellis not present in the subframe. By processing CSI-RS measurements upondetecting that CSI-RS transmissions for the LA SCell are present on thecorresponding subframes, the accuracy of the CSI-RS measurements on theLA SCell is substantially improved.

In some embodiments, in order to determine whether a CSI-RS transmissionfrom the LA SCell of the wireless device is present in the subframe, thewireless device further operates to determine whether the wirelessdevice has received a downlink scheduling grant for the LA SCell for thesubframe, wherein determining that a downlink scheduling grant has beenreceived for the LA SCell for the subframe indicates that a CSI-RStransmission is present in the subframe.

In some embodiments, in order to determine whether a CSI-RS transmissionfrom the LA SCell of the wireless device is present in the subframe, thewireless device further operates to determine whether the subframe is adiscovery subframe for the LA SCell, wherein determining that thesubframe is a discovery subframe for the LA SCell indicates that aCSI-RS transmission is present in the subframe.

In some embodiments, in order to determine whether a CSI-RS transmissionfrom the LA SCell of the wireless device is present in the subframe, thewireless device further operates to determine whether a Downlink ControlInformation (DCI) message received by the wireless device includes anindication that a CSI-RS transmission is present in the subframe.

In some embodiments, in order to determine whether a CSI-RS transmissionfrom the LA SCell of the wireless device is present in the subframe, thewireless device further operates to determine whether the wirelessdevice has received an uplink grant for the LA SCell for the subframe,wherein determining that the wireless device has received an uplinkgrant for the LA SCell for the subframe indicates that a CSI-RStransmission is not present in the subframe.

In some embodiments, the wireless device further operates to, upondetermining that transmission from the LA SCell is present in thesubframe, perform a first type of interference measurement on configuredCSI Interference Measurement (CSI-IM) resources in the subframe.Otherwise, the wireless device operates to perform a second type ofinterference measurement on the configured CSI-IM resources in thesubframe.

In some embodiments, the wireless device further operates to send a CSIreport to a network node of the cellular communications network based ona latest available CSI-RS measurement for the LA SCell and the firsttype of interference measurement upon determining that transmission fromthe LA SCell is present in the subframe and, otherwise, send a CSIreport to the network node of the cellular communications network basedon the latest available CSI-RS measurement for the LA SCell and thesecond type of interference measurement.

In some embodiments, the wireless device further operates to determinewhether a latest available valid CSI-RS measurement for the LA SCell isolder than a predefined age threshold. Upon determining that the latestavailable valid CSI-RS measurement for the LA SCell is older than thepredefined age threshold, the wireless device operates to send anindication to the network node of the cellular communications networkthat the latest available valid CSI-RS measurement is older than thepredefined age threshold. Upon determining that transmission from the LASCell is present in the subframe, the wireless device operates to send aCSI report to a network node of the cellular communications networkbased on the latest available valid CSI-RS measurement for the subframeand the first type of interference measurement upon determining thattransmission from the LA SCell is present in the subframe and,otherwise, send a CSI report to a network node of the cellularcommunications network based on the latest available valid CSI-RSmeasurement for the subframe and the second type of interferencemeasurement.

In some embodiments, the wireless device further operates to send a CSIreport to a network node of the cellular communications network.

Embodiments of a method of operation of a wireless device are alsodisclosed.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the embodiments in association withthe accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 illustrates the basic Long Term Evolution (LTE) downlink physicalresource;

FIG. 2 illustrates the LTE downlink frame structure;

FIG. 3 illustrates a LTE downlink system with a Control Format Indicator(CFI) of 3;

FIG. 4 illustrates Carrier Aggregation (CA);

FIG. 5 is a general illustration of a Listen-Before-Talk (LBT)mechanism;

FIG. 6 illustrates a License Assisted Secondary Cell (LA SCell)operating in an unlicensed frequency spectrum;

FIG. 7 illustrates one example of a cellular communications networkaccording to embodiments of the present disclosure;

FIG. 8 illustrates the operation of a Radio Access Network (RAN) nodeand a wireless device to provide Channel State Information (CSI)reporting for a LA SCell according to some embodiments of the presentdisclosure;

FIGS. 9A through 9C are flow charts that illustrate the operation awireless device to provide CSI Reference Symbol (CSI-RS) measurement andCSI reporting for a LA SCell according to some embodiments of thepresent disclosure;

FIGS. 10 through 13 illustrate the process of FIG. 9A in which differentCSI-RS detection mechanisms are used to determine whether CSI-RStransmissions from the LA SCell are present before processing CSI-RSmeasurements according to some embodiments of the present disclosure;

FIG. 14 graphically illustrates an example of the use of the embodimentsof FIGS. 10 through 13 to detect whether CSI-RS transmissions on the LASCell are present in a subframe according to some embodiments of thepresent disclosure;

FIG. 15 is a flow chart that illustrates the operation of a wirelessdevice to perform different types of interference measurements dependingon whether CSI-RS transmissions are present in the subframe according tosome embodiments of the present disclosure;

FIG. 16 illustrates the CSI reporting step of FIG. 15 in more detailaccording to some embodiments of the present disclosure;

FIG. 17 is a flow chart that illustrates the operation of a RAN node tosend an indication according to some embodiments of the presentdisclosure;

FIGS. 18 and 19 are block diagrams of a base station according to someembodiments of the present disclosure; and

FIGS. 20 and 21 are block diagrams of a wireless device according tosome embodiments of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent information to enable thoseskilled in the art to practice the embodiments and illustrate the bestmode of practicing the embodiments. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the disclosure and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

Systems and methods relating to accurate Channel State Information (CSI)measurements for a License Assisted Secondary Cell (LA SCell) aredisclosed herein. Notably, the embodiments described herein focus onThird Generation Partnership Project (3GPP) Long Term Evolution (LTE)and, as such, 3GPP LTE terminology is oftentimes used. However, thepresent disclosure is not limited to LTE.

According to some embodiments of the present disclosure, a UserEquipment device (UE) is buffering measurements based on at leastperiodically configured CSI Reference Symbol (CSI-RS) transmissions andpotentially also CSI Interference Measurement (CSI-IM) resources tocompute CSI (e.g., Channel Quality Information (CQI), rank, PrecodingMatrix Indicator (PMI)) for a given CSI process. Since the presence ofCSI-RS is not guaranteed on a LA SCell, the UE first detects on the LASCell whether the CSI-RS from the LA SCell is present in a subframebefore taking the CSI-RS measurement in this subframe on the LA SCellinto account in further CSI processing and CSI reporting. This detectioncan performed either implicitly (e.g., by UE blind detection) orexplicitly (e.g., by receiving a control message).

In a first embodiment, the UE first detects a downlink scheduling grantfor a LA SCell in a subframe where the UE has been configured to measureon CSI-RS associated with a given CSI process. If the detection issuccessful, the UE will take the CSI measurement from this subframe intoaccount in the CSI processing and subsequent CSI reporting for the LASCell. Otherwise, the UE discards the measurement in this subframe oravoids to perform a measurement altogether in this subframe. Thedownlink grant is received on the Physical Downlink Control Channel(PDCCH) or the enhanced PDCCH (EPDCCH) on the LA SCell (self-scheduling)or is cross-carrier scheduled from another cell (Primary Cell (PCell) ornon-LA SCell).

In a second embodiment, the UE first determines that the subframe whereit has been configured to measure on CSI-RS associated with a given CSIprocess also contains a discovery signal burst consisting of at leastPrimary and/or Secondary Synchronization Signals (PSS/SSS) andpotentially also CSI-RS for discovery purposes. Hence, since the LASCell subframe contains these signals, it is a guaranteed to be adownlink subframe and the UE uses the associated CSI-RS measurementsfrom this subframe.

In a third embodiment, a Downlink Control Information (DCI) message istransmitted, either a self-scheduling message on the LA SCell or across-carrier scheduling DCI to schedule the LA SCell. This message doesnot contain a scheduling of a Physical Downlink Shared Channel (PDSCH)transmission, but the message contains an indication that the subframewhere the DCI is received is a downlink subframe on the LA SCell andthat the UE may measure CSI-RS in this subframe, if the subframe is alsoa subframe where one of the configured CSI processes has an associatedCSI-RS transmission from the enhanced or evolved Node B (eNB). Thismessage may be a Physical Uplink Shared Channel (PUSCH) scheduling grantor it may be an invalid PDSCH scheduling assignment, such as with a zerotransport block size or any other code point in the DCI message thatdoes not correspond to a valid PDSCH transmission with non-zerotransport block size. The DCI message may further contain a dynamicconfiguration of the CSI-RS resource(s) to be used. The CSI-RSresource(s) may be selected by a full set of CSI-RSs that are availableor a subset of the CSI-RSs.

In a fourth embodiment, the UE receives an uplink grant for the LA SCellin a subframe n, and the associated PUSCH should be transmitted insubframe n+k. In LTE frame structure 1 (Frequency Division Duplex(FDD)), the value of k=4, as an example. If the UE is configured tomeasure on CSI-RS for any of its CSI processes in subframe n+k, thenthis is an uplink subframe and the UE shall not perform CSI-RSmeasurements in this subframe.

In a fifth embodiment, two different interference measurements types, Aand B, are administered by the UE based on the same configured CSI-IMresource or two separate CSI-IM configurations. One measurement A isperformed for which the UE has a guaranteed downlink, by e.g. schedulinga downlink PDSCH message as in embodiment one, a Dedicated ReferenceSignal (DRS) subframe as in embodiment 2 or any other indicator as inembodiment 3. Another interference measurement B, for which processing(e.g., time averaging) is kept separate to measurement A, is performedin subframes where a CSI-IM is present (by configuration) but it isuncertain whether the serving eNB has grabbed the downlink channel.Hence, there is no indication from the network to the UE. Theinterference measured by measurement type B can thus be used to measureinterference from LA SCells not coordinated with the serving LA SCell,or from other transmitting nodes in the unlicensed band, such as Wi-Finodes. Two separate reports will then be sent back to the serving node,one for each interference measurement type A and B.

For the case when the UE is supposed to report either a periodic CSIreporting or an aperiodic CSI, the UE may use the latest available validCSI-RS measurement that it has measured and combine this measurementwith a newer interference measurement. The UE could for such a casereport the CSI based on only an interference measurement type Bmeasurement. Another alternative is that if the UE has a valid CSI-RSmeasurement report from the same subframe as a CSI-IM measurement, theUE would instead report a CSI report based on an interferencemeasurement type A measurement. An additional embodiment is if the lastvalid CSI-RS measurement is too old the UE would directly report a valueindicating this fact, for example that the CQI is out of range. Whetherthe CSI-RS is too old or not could be a configured value for the UE or aspecific number of subframes that is static.

FIG. 7 illustrates a cellular communications network 10 according tosome embodiments of the present disclosure. In this example, thecellular communications network 10 includes base stations 12-1 and 12-2,which in LTE are referred to as eNBs, controlling corresponding macrocells 14-1 and 14-2. The base stations 12-1 and 12-2 are generallyreferred to herein collectively as base stations 12 and individually asbase station 12. Likewise, the macro cells 14-1 and 14-2 are generallyreferred to herein collectively as macro cells 14 and individually asmacro cell 14. The cellular communications network 10 also includes anumber of low power nodes 16-1 through 16-4 controlling correspondingsmall cells 18-1 through 18-4. In LTE, the low power nodes 16-1 through16-4 can be small base stations (such as pico or femto base stations) orRemote Radio Heads (RRHs), or the like. Notably, while not illustrated,one or more of the small cells 18-1 through 18-4 may alternatively beprovided by the base station 12. The low power nodes 16-1 through 16-4are generally referred to herein collectively as low power nodes 16 andindividually as low power node 16. Likewise, the small cells 18-1through 18-4 are generally referred to herein collectively as smallcells 18 and individually as small cell 18. The base stations 12 (andoptionally the low power nodes 16) are connected to a core network 20.

The base stations 12 and the low power nodes 16 provide service towireless devices 22-1 through 22-5 in the corresponding cells 14 and 18.The wireless devices 22-1 through 22-5 are generally referred to hereincollectively as wireless devices 22 and individually as wireless device22. In LTE, the wireless devices 22 are referred to as UEs.

In this example, the macro cells 14 are provided in the licensedfrequency spectrum (i.e., in the frequency spectrum dedicated for thecellular communications network 10), whereas one or more (and possiblyall) of the small cells 18 are provided in an unlicensed frequencyspectrum (e.g., the 5 Gigahertz (GHz) frequency spectrum). Using thewireless device 22-1 as an example, the macro cell 14-1 is a PCell ofthe wireless device 22-1 and the small cell 18-1 is a LA SCell of thewireless device 22-1. Thus, in this context, the macro cell 14-1 issometimes referred to herein as the PCell 14-1 of the wireless device22-1, and the small cell 18-1 is sometimes referred to herein as the LASCell 18-1 of the wireless device 22-1.

The cellular communications network 10 (e.g., the base station 12-1)configures one or more CSI processes of the wireless device 22-1 toperform CSI measurements (and to provide resulting CSI reports) onCSI-RS resources and potentially CSI-IM resources. The CSI-RS resources(and potentially the CSI-IM resources) are at least periodicallyconfigured to compute CSI (e.g., CQI, rank, and PMI) for a given CSIprocess. However, because the LA SCell 18-1 is provided in theunlicensed frequency band, a Listen-Before-Talk (LBT) scheme is utilizedto determine whether transmissions on the LA SCell 18-1 are permitted atany particular time. Therefore, particularly for periodicconfigurations, the presence of CSI-RS transmissions in a subframe inwhich the wireless device 22-1 is configured to perform CSI measurementsfor the LA SCell 18-1 is not guaranteed. Thus, in order to preventcorrupt CSI measurements, the wireless device 22-1 detects whetherCSI-RS transmissions from the LA SCell 18-1 are present in the subframebefore taking CSI-RS measurements in the subframe on the LA SCell 18-1into account for further CSI processing and CSI reporting. As discussedbelow, the detection of the presence of CSI-RS transmissions on the LASCell 18-1 in the subframe can be implicit (e.g., by blind detection bythe wireless device 22-1) or explicit (e.g., by receiving a controlmessage from, e.g., the base station 12-1 on the PCell 14-1 of thewireless device 22-1).

FIG. 8 illustrates the operation of a Radio Access Network (RAN) node 24(e.g., the base station 12-1 or the low power node 16-1) and thewireless device 22-1 with respect to CSI measurements and CSI reportingfor the LA SCell 18-1 according to some embodiments of the presentdisclosure. As illustrated, the RAN node 24 provides a CSI configurationto the wireless device 22-1 for the LA SCell 18-1 of the wireless device22-1 (step 100). The CSI configuration is, in this example, a periodicCSI configuration that configures periodic CSI-RS resources and,potentially, periodic CSI-IM resources for a CSI process at the wirelessdevice 22-1. For example, the CSI configuration may configure particularCSI-RS and CSI-IM resources for measurement on the LA SCell 18-1 every Tsubframes, where T={5,10,20,40,80}.

The wireless device 22-1 performs CSI measurements on the LA SCell 18-1and generates CSI report(s) for the LA SCell 18-1 while restricting theuse of CSI-RS measurements to subframes for which CSI-RS transmissionsare detected (i.e., determined to be present) (step 102). The wirelessdevice 22-1 sends the CSI report(s) for the LA SCell 18-1 to the RANnode 24 (step 104).

FIGS. 9A through 9C illustrate steps 102 and 104 of FIG. 8 in moredetail according to some embodiments of the present disclosure. Withrespect to a periodic CSI-RS configuration, this process is performedfor each subframe for which CSI-RS is configured for the wireless device22-1. Note, however, that this process may also be performed foraperiodic CSI-RS configuration.

As illustrated, the wireless device 22-1 detects whether a CSI-RStransmission is present on the LA SCell 18-1 in a subframe for whichCSI-RS is configured for the wireless device 22-1 either via periodic oraperiodic CSI-RS configuration (step 200). As discussed below, thisdetection may be implicit or explicit. If a CSI-RS transmission on theLA SCell 18-1 for the subframe is detected, the wireless device 22-1processes a CSI-RS measurement for the LA SCell 18-1, e.g., in theconventional manner (step 202). The processing of the CSI-RS measurementmay include, for example, combining the CSI-RS measurement on the LASCell 18-1 with one or more previous CSI-RS measurements on the LA SCell18-1. Based on the CSI-RS measurement, the wireless device 22-1generates a CSI report and sends the CSI report to, e.g., the basestation 12-1 controlling the PCell 14-1 of the wireless device 22-1(step 104).

Conversely, if a CSI-RS transmission on the LA SCell 18-1 in thesubframe is not detected in step 200, the wireless device 22-1 refrainsfrom processing a CSI-RS measurement on the LA SCell 18-1 for thesubframe (step 204). For example, if a CSI-RS measurement has alreadybeen performed on the LA SCell 18-1 for the subframe, this CSI-RSmeasurement is discarded. As another example, the wireless device 22-1refrains from performing a CSI-RS measurement on the LA SCell 18-1 forthe subframe. The wireless device 22-1 may then, in some embodiments,send a CSI report based on, e.g., a latest available CSI-RS measurementfor the LA SCell 18-1 (step 104).

Notably, in the process of FIG. 9A, the CSI-RS measurement on the LASCell 18-1 for the subframe may be performed prior to step 200 orperformed only after detecting CSI-RS on the LA SCell 18-1 for thesubframe in step 200. In this regard, FIG. 9B illustrates a process thatis similar to that of FIG. 9A but where the CSI-RS measurement on the LASCell 18-1 for the subframe is performed prior to detecting whether aCSI-RS transmission is present on the LA SCell 18-1 for the subframeaccording to some embodiments of the present disclosure. As illustrated,the wireless device 22-1 performs a CSI-RS measurement on the configuredresource elements in a subframe for which CSI-RS is configured for thewireless device 22-1 either via periodic or aperiodic CSI-RSconfiguration (i.e., the wireless device 22-1 performs a CSI-RSmeasurement on the resource elements in the subframe in which CSI-RS issupposed to be transmitted on the LA SCell 18-1) (step 300). Thewireless device 22-1 detects whether a CSI-RS transmission is present onthe LA SCell 18-1 in the subframe (step 302). As discussed below, thisdetection may be implicit or explicit. If a CSI-RS transmission on theLA SCell 18-1 for the subframe is detected, the wireless device 22-1processes a CSI-RS measurement for the LA SCell 18-1, e.g., in theconventional manner (step 304). Based on the CSI-RS measurement, thewireless device 22-1 generates a CSI report and sends the CSI report to,e.g., the base station 12-1 controlling the PCell 14-1 of the wirelessdevice 22-1 (step 104).

Conversely, if a CSI-RS transmission on the LA SCell 18-1 in thesubframe is not detected in step 302, the wireless device 22-1 refrainsfrom processing the CSI-RS measurement on the LA SCell 18-1 for thesubframe (step 306). For example, the wireless device 22-1 may discardthe CSI-RS measurement performed in step 300. The wireless device 22-1may then, in some embodiments, send a CSI report based on, e.g., alatest available CSI-RS measurement for the LA SCell 18-1 (step 104).

FIG. 9C illustrates a process that is similar to that of FIG. 9A butwhere the CSI-RS measurement on the LA SCell 18-1 for the subframe isperformed after detecting that a CSI-RS transmission is present on theLA SCell 18-1 for the subframe according to some embodiments of thepresent disclosure. As illustrated, the wireless device 22-1 detectswhether a CSI-RS transmission is present on the LA SCell 18-1 in asubframe for which CSI-RS is configured for the wireless device 22-1either via periodic or aperiodic CSI-RS configuration (step 400). Asdiscussed below, this detection may be implicit or explicit. If a CSI-RStransmission on the LA SCell 18-1 for the subframe is detected, thewireless device 22-1 performs a CSI-RS measurement on the LA SCell 18-1for the subframe (step 402). The wireless device 22-1 processes theCSI-RS measurement for the LA SCell 18-1, e.g., in the conventionalmanner (step 404). Based on the CSI-RS measurement, the wireless device22-1 generates a CSI report and sends the CSI report to, e.g., the basestation 12-1 controlling the PCell 14-1 of the wireless device 22-1(step 104).

Conversely, if a CSI-RS transmission on the LA SCell 18-1 in thesubframe is not detected in step 400, the wireless device 22-1 refrainsfrom performing a CSI-RS measurement on the LA SCell 18-1 for thesubframe (step 406). The wireless device 22-1 may then, in someembodiments, send a CSI report based on, e.g., a latest available CSI-RSmeasurement for the LA SCell 18-1 (step 104).

FIGS. 10 through 13 illustrate examples of the first through fourthembodiments described above, respectively. Notably, while theseembodiments are described separately, any combination of the differentCSI-RS detection schemes illustrated in FIGS. 10 through 13 may be usedby the wireless device 22-1 to detect CSI-RS transmission. Inparticular, FIG. 10 illustrates the process of FIG. 9A in which CSI-RSdetection is performed by detecting a downlink scheduling grant for thewireless device 22-1 on the LA SCell 18-1 for a subframe for which thewireless device 22-1 is configured to perform CSI-RS measurement on theLA SCell 18-1 according to some embodiments of the present disclosure.As illustrated, the wireless device 22-1 detects whether the wirelessdevice 22-1 has received a downlink scheduling grant on the LA SCell18-1 for a subframe for which CSI-RS is configured for the wirelessdevice 22-1 either via periodic or aperiodic CSI-RS configuration (step500). The downlink scheduling grant is only sent if the LA SCell 18-1 ispermitted to transmit in the downlink for the subframe. As such,detecting of the downlink scheduling grant is an implicit indicationthat CSI-RS transmissions on the LA SCell 18-1 are present in thesubframe. The downlink scheduling grant may be received on PDCCH orEPDCCH on the LA SCell 18-1 (i.e., self-scheduling) or received fromanother cell (e.g., from the PCell 14-1 of the wireless device 22-1 or anon-LA SCell of the wireless device 22-1) via cross-carrier scheduling.

If a downlink scheduling grant is detected (i.e., if a CSI-RStransmission on the LA SCell 18-1 for the subframe is detected), thewireless device 22-1 processes a CSI-RS measurement for the LA SCell18-1, e.g., in the conventional manner (step 502). The processing of theCSI-RS measurement may include, for example, combining the CSI-RSmeasurement on the LA SCell 18-1 with one or more previous CSI-RSmeasurements on the LA SCell 18-1. Based on the CSI-RS measurement, thewireless device 22-1 generates a CSI report and sends the CSI report to,e.g., the base station 12-1 controlling the PCell 14-1 of the wirelessdevice 22-1 (step 104).

Conversely, if a downlink scheduling grant is not detected in step 500(i.e., if a CSI-RS transmission on the LA SCell 18-1 in the subframe isnot detected), the wireless device 22-1 refrains from processing aCSI-RS measurement on the LA SCell 18-1 for the subframe (step 504). Forexample, if a CSI-RS measurement has already been performed on the LASCell 18-1 for the subframe, this CSI-RS measurement is discarded. Asanother example, the wireless device 22-1 refrains from performing aCSI-RS measurement on the LA SCell 18-1 for the subframe. The wirelessdevice 22-1 may then, in some embodiments, send a CSI report based on,e.g., a latest available CSI-RS measurement for the LA SCell 18-1 (step104).

FIG. 11 illustrates the process of FIG. 9A in which CSI-RS detection isperformed by detecting that a subframe on the LA SCell 18-1 for whichthe wireless device 22-1 is configured to perform CSI-RS measurement onthe LA SCell 18-1 is a discovery subframe according to some embodimentsof the present disclosure. As illustrated, the wireless device 22-1detects whether a subframe for which CSI-RS is configured for thewireless device 22-1 on the LA SCell 18-1 is a discovery subframe (step600). More specifically, starting with LTE Release 12, SCellsperiodically transmit discovery signals in corresponding discoverysubframes to enable wireless devices to detect those SCells. This isparticularly important since SCells can operate according to an on/offscheme. When a SCell is not currently serving any wireless devices, theSCell may be turned off to, e.g., conserve power. When off, the SCellstill periodically transmits a discovery signal in correspondingdiscovery subframes. The discovery signal is designed such that itincludes PSS/SSS as well as CSI-RS. As such, upon detecting that thesubframe is a discovery subframe (i.e., upon detecting a discoverysignal on the subframe), this is an implicit indication to the wirelessdevice 22-1 that the CSI-RS transmissions are present in the subframe.

If a discovery subframe is detected (i.e., if a CSI-RS transmission onthe LA SCell 18-1 for the subframe is detected), the wireless device22-1 processes a CSI-RS measurement for the LA SCell 18-1, e.g., in theconventional manner (step 602). The processing of the CSI-RS measurementmay include, for example, combining the CSI-RS measurement on the LASCell 18-1 with one or more previous CSI-RS measurements on the LA SCell18-1. Based on the CSI-RS measurement, the wireless device 22-1generates a CSI report and sends the CSI report to, e.g., the basestation 12-1 controlling the PCell 14-1 of the wireless device 22-1(step 104).

Conversely, if a discovery subframe is not detected in step 600 (i.e.,if a CSI-RS transmission on the LA SCell 18-1 in the subframe is notdetected), the wireless device 22-1 refrains from processing a CSI-RSmeasurement on the LA SCell 18-1 for the subframe (step 604). Forexample, if a CSI-RS measurement has already been performed on the LASCell 18-1 for the subframe, this CSI-RS measurement is discarded. Asanother example, the wireless device 22-1 refrains from performing aCSI-RS measurement on the LA SCell 18-1 for the subframe. The wirelessdevice 22-1 may then, in some embodiments, send a CSI report based on,e.g., a latest available CSI-RS measurement for the LA SCell 18-1 (step104).

FIG. 12 illustrates the process of FIG. 9A in which CSI-RS detection isperformed by detecting a DCI message including an indication that CSI-RStransmissions are present in the subframe on the LA SCell 18-1 for whichthe wireless device 22-1 is configured to perform CSI-RS measurement onthe LA SCell 18-1 according to some embodiments of the presentdisclosure. As illustrated, the wireless device 22-1 detects whether aDCI message has been received that includes an indication that CSI-RStransmissions are present in a subframe for which CSI-RS is configuredfor the wireless device 22-1 on the LA SCell 18-1 (step 700). The DCImessage may be either a self-scheduling message received on the LA SCell18-1 or a cross-carrier scheduling DCI message to schedule the LA SCell18-1 received on another cell (e.g., the PCell 14-1 of the wirelessdevice 22-1 or a non-LA SCell of the wireless device 22-1). This DCImessage does not contain a scheduling of a PDSCH transmission for thewireless device 22-1 on the LA SCell 18-1. Rather, this DCI messageincludes an indication that the subframe where the DCI message isreceived is a downlink subframe on the LA SCell 18-1 and that thewireless device 22-1 may measure CSI-RS in this subframe. This DCImessage may be, e.g., a PUSCH scheduling grant or an invalid PDSCHscheduling assignment, such as with a zero transport block size or anyother code point in the DCI message that does not correspond to a validPDSCH transmission with non-zero transport block size. For an aperiodicCSI configuration, the DCI message may further contain a dynamicconfiguration of the CSI-RS resource(s) to be used. The CSI-RSresource(s) may be selected from a full set of CSI-RSs that areavailable or a subset of the CSI-RSs.

If a DCI message including the indication that CSI-RS transmissions onthe LA SCell 18-1 are present in the subframe is detected (i.e., if aCSI-RS transmission on the LA SCell 18-1 for the subframe is detected),the wireless device 22-1 processes a CSI-RS measurement for the LA SCell18-1, e.g., in the conventional manner (step 702). The processing of theCSI-RS measurement may include, for example, combining the CSI-RSmeasurement on the LA SCell 18-1 with one or more previous CSI-RSmeasurements on the LA SCell 18-1. Based on the CSI-RS measurement, thewireless device 22-1 generates a CSI report and sends the CSI report to,e.g., the base station 12-1 controlling the PCell 14-1 of the wirelessdevice 22-1 (step 104).

Conversely, if a DCI message including the indication that CSI-RStransmissions on the LA SCell 18-1 are present in the subframe is notdetected in step 700 (i.e., if a CSI-RS transmission on the LA SCell18-1 in the subframe is not detected), the wireless device 22-1 refrainsfrom processing a CSI-RS measurement on the LA SCell 18-1 for thesubframe (step 704). For example, if a CSI-RS measurement has alreadybeen performed on the LA SCell 18-1 for the subframe, this CSI-RSmeasurement is discarded. As another example, the wireless device 22-1refrains from performing a CSI-RS measurement on the LA SCell 18-1 forthe subframe. The wireless device 22-1 may then, in some embodiments,send a CSI report based on, e.g., a latest available CSI-RS measurementfor the LA SCell 18-1 (step 104).

FIG. 13 illustrates the process of FIG. 9A in which CSI-RS detection isperformed by detecting whether the wireless device 22-1 has received anuplink scheduling grant for the LA SCell 18-1 for a subframe for whichthe wireless device 22-1 is configured to perform CSI-RS measurement onthe LA SCell 18-1 according to some embodiments of the presentdisclosure. As illustrated, the wireless device 22-1 detects whether thewireless device 22-1 has received an uplink scheduling grant for the LASCell 18-1 for a subframe for which the wireless device 22-1 isconfigured to perform CSI-RS measurement on the LA SCell 18-1 (step800). More specifically, if the wireless device 22-1 receives an uplinkscheduling grant for the LA SCell 18-1 in a subframe n, the associateduplink transmission (i.e., the associated PUSCH for LTE) should betransmitted in subframe n+k. In LTE frame structure 1 (FDD), the valueof k=4, as an example. Therefore, the uplink scheduling grant is animplicit indication that CSI-RS transmissions are not present insubframe n+k. Conversely, if the wireless device 22-1 has not receivedan uplink scheduling grant for the subframe (i.e., has not received anuplink scheduling grant in subframe n for an uplink transmission on theLA SCell 18-1 during subframe n+k, then this is an implicit indicationthat CSI-RS transmissions are present in subframe n+k.

If the wireless device 22-1 has not received an uplink scheduling grantfor the subframe (i.e., if a CSI-RS transmission on the LA SCell 18-1for the subframe is detected), the wireless device 22-1 processes aCSI-RS measurement for the LA SCell 18-1, e.g., in the conventionalmanner (step 802). The processing of the CSI-RS measurement may include,for example, combining the CSI-RS measurement on the LA SCell 18-1 withone or more previous CSI-RS measurements on the LA SCell 18-1. Based onthe CSI-RS measurement, the wireless device 22-1 generates a CSI reportand sends the CSI report to, e.g., the base station 12-1 controlling thePCell 14-1 of the wireless device 22-1 (step 104).

Conversely, if the wireless device 22-1 has received an uplinkscheduling grant for the subframe in step 800 (i.e., if a CSI-RStransmission on the LA SCell 18-1 in the subframe is not detected), thewireless device 22-1 refrains from processing a CSI-RS measurement onthe LA SCell 18-1 for the subframe (step 804). For example, if a CSI-RSmeasurement has already been performed on the LA SCell 18-1 for thesubframe, this CSI-RS measurement is discarded. As another example, thewireless device 22-1 refrains from performing a CSI-RS measurement onthe LA SCell 18-1 for the subframe. The wireless device 22-1 may then,in some embodiments, send a CSI report based on, e.g., a latestavailable CSI-RS measurement for the LA SCell 18-1 (step 104).

Again, while FIGS. 10 through 13 illustrate different ways to detectwhether CSI-RS transmissions are present in a subframe, any combinationof two or more of the detection mechanisms in FIGS. 10 through 13 may beused together, if desired. For example, the detection mechanism of FIG.13 may be used to identify subframes in which CSI-RS transmissions arenot present (due to a scheduled uplink transmission on the LA SCell18-1), and the detection mechanism(s) of any one or more of FIGS. 10through 12 may then be used to determine whether CSI-RS transmissionsare present on those subframes that do not have scheduled uplinktransmissions.

In this regard, FIG. 14 illustrates an example of five frames for thePCell 14-1 and the LA SCell 18-1 where cross-carrier scheduling is used.It can be seen that only in discovery (i.e., DRS) subframes and insubframes where there is a PDSCH transmission will the wireless device22-1 assume the CSI-RS measurement is valid (i.e., assume that CSI-RStransmissions on the LA SCell 18-1 are present) and utilize thisinformation in CSI processing. More specifically, as illustrated,CSI-RSs are periodically configured for the wireless device 22-1 for theLA SCell 18-1 in the third subframe of each radio frame. In frames n−2and n+2, the wireless device 22-1 detects, or determines, that CSI-RStransmissions are not present on the third subframes of those framesbecause: (a) the wireless device 22-1 did not receive a downlinkscheduling grant for the LA SCell 18-1 for those subframes, (b) thewireless device 22-1 did not detect that those subframes are discoverysubframes for the LA SCell 18-1, and (c) the wireless device 22-1 didnot receive DCI messages on the PCell 14-1 that include an indicationthat CSI-RS transmissions are present on those subframes. Conversely, inframes n−1 and n+1, the wireless device 22-1 detects that CSI-RStransmissions are present on the third subframes of those frames as aresult of reception of corresponding DCI messages including indicationsthat CSI-RS transmissions are present on those subframes. In frame n,the wireless device 22-1 detects that CSI-RS transmissions are presentin the third subframe of that frame by detecting a downlink schedulinggrant for that subframe. In addition, the wireless device 22-1 detectsthat CSI-RS transmissions are present in the first subframes of framesn−2 and n+2 by detecting discovery signals/bursts in those subframes.

Thus far, much of the discussion has focused on CSI-RS measurements.However, the CSI-RS detection schemes disclosed herein can additionallyor alternatively be used with respect to CSI-IM measurements. Strictlyspeaking, CSI-IM is not subject to LBT schemes because CSI-IM are ZeroPower (ZP) CSI-RSs (i.e., the LA SCell 18-1 does not transmit on theCSI-IM resources). However, there is still an issue in that CSI-IMmeasurements will be different depending on whether the LA SCell 18-1 istransmitting in the subframe or not. Typically, CSI-IM measurements aremore important when the LA SCell 18-1 is transmitting when selectingtransmit parameters (e.g., Modulation and Coding Scheme (MCS)) for theLA SCell 18-1.

In this regard, FIG. 15 illustrates steps 102 and 104 of FIG. 8 in moredetail according to some embodiments of the present disclosure in whichthe CSI-RS transmission detection schemes disclosed above are utilizedto perform different types of interference measurements depending onwhether CSI-RS transmissions are present in the subframe. Note thatwhile FIG. 15 is described in relation to steps 102 and 104 of FIG. 8,the process of FIG. 15 is not limited thereto.

As illustrated, the wireless device 22-1 detects whether transmission ispresent on the LA SCell 18-1 in a subframe for which CSI-IM (andpotentially CSI-RS) is configured for the wireless device 22-1 eithervia periodic or aperiodic CSI-RS configuration (step 900). Thisdetection may use, for example, any one or any combination of thedetection schemes disclosed above, but is not limited thereto. Iftransmission on the LA SCell 18-1 for the subframe is detected, thewireless device 22-1 performs a Type A interference measurement on theconfigured CSI-IM resources for the subframe (step 902). The Type Ainterference measurement is a CSI-IM measurement when the wirelessdevice 22-1 has detected that the LA SCell 18-1 is transmitting (e.g.,by detecting that CSI-RS transmissions are present in the subframe).Otherwise, the wireless device 22-1 performs a Type B interferencemeasurement on the configured CSI-IM resources for the subframe (step904). The Type B interference measurement is a CSI-IM measurement whenthe wireless device 22-1 knows that the LA SCell 18-1 is nottransmitting or is uncertain as to whether the LA SCell 18-1 istransmitting. The interference measured by the Type B interferencemeasurement can thus be used to measure interference from LA SCells 18not coordinated with the serving LA SCell 18-1, or from othertransmitting nodes in the unlicensed band, such as Wi-Fi nodes. Notably,the CSI-IM resources for the two types of interference measurements maybe the same CSI-IM resources or, alternatively, different CSI-IMresources may be configured for the different types of interferencemeasurements. Processing (e.g., time averaging) is kept separate for theType A interference measurement and the Type B interference measurement.

The wireless device 22-1 then sends a CSI report(s) to the network(e.g., to the base station 12-1 serving the PCell 14-1 or to the lowpower node 16-1 serving the LA SCell 18-1) (step 104). In someembodiments, the wireless device 22-1 sends separate CSI reports forType A and Type B interference measurements. For example, if the latestavailable (valid) CSI-RS measurement is made in the same subframe fromwhich the Type A interference measurement is made, the CSI report isbased on a latest available (valid) CSI-RS measurement (as discussedabove) and the Type A interference measurement. Otherwise, the CSIreport is based on, e.g., the latest available (valid) CSI-RSmeasurement for the LA SCell 18-1 and the Type B interferencemeasurement. The latest available (valid) CSI-RS measurement is thelatest available CSI-RS measurement for a subframe for which CSI-RStransmission is detected for the LA SCell 18-1 (which may be the currentsubframe or some previous subframe), as discussed above.

FIG. 16 illustrates step 104 of FIG. 15 in more detail according to oneembodiment of the present disclosure. As illustrated, the wirelessdevice 22-1 determines whether the latest available (valid) CSI-RSmeasurement for the LA SCell 18-1 is too old (step 1000). Morespecifically, an age threshold (e.g., a statically defined number ofsubframes) may be predefined by, e.g., standard, or configured by, e.g.,the network operator. The latest available (valid) CSI-RS measurement tothe latest CSI-RS measurement is made on the LA SCell 18-1 for asubframe for which CSI-RS transmission was detected for the LA SCell18-1. This subframe may be the current subframe or some previoussubframe.

If the age of the latest available (valid) CSI-RS measurement for the LASCell 18-1 is less than the age threshold, then the wireless device 22-1sends a CSI report based on a latest available (valid) CSI-RSmeasurement for the LA SCell 18-1 and either the Type A interferencemeasurement or the Type B interference measurement performed in step 902or 904, depending on whether the latest available (valid) CSI-RSmeasurement is made in the same subframe from which the Type Ainterference measurement is made (step 1002). More specifically, if thelatest available (valid) CSI-RS measurement is made in the same subframefrom which the Type A interference measurement is made, the CSI reportis based on the latest available (valid) CSI-RS measurement (asdiscussed above) and the Type A interference measurement. Otherwise, theCSI report is based on, e.g., the latest available (valid) CSI-RSmeasurement for the LA SCell 18-1 and the Type B interferencemeasurement. Conversely, if the age of the latest available (valid)CSI-RS measurement for the LA SCell 18-1 is greater than the agethreshold, then the latest available CSI-RS measurement is determined tobe too old for reporting, and the wireless device 22-1 sends acorresponding indication to the network (e.g., to the base station 12-1serving the PCell 14-1 or to the low power node 16-1 serving the LASCell 18-1) (step 1004). This indication may be an indication that theCQI is out of range.

Much of the description above focuses on the operation of the wirelessdevice 22. However, at least in some embodiments, the RAN node 24includes functionality to enable the wireless device 22 to detectwhether CSI-RS transmissions from a LA SCell 18 are present in asubframe. In this regard, FIG. 17 illustrates the operation of the RANnode 24 to provide an indication of whether CSI-RS transmissions from aLA SCell 18 are present in a subframe according to some embodiments ofthe present disclosure. The RAN node 24 may be either the base station12 serving the PCell 14 of the wireless device 22, a low power node 16serving a non-LA SCell of the wireless device 22, or the low power node16 serving the LA SCell 18 of the wireless device 22.

As illustrated, the RAN node 24 determines whether a LA SCell 18 cantransmit, or is permitted to transmit, in a subframe using a LBT scheme(step 1100). In some embodiments, this determination is made only forthose subframes for which the wireless device 22 is configured toperform CSI-RS, and potentially CSI-IM, measurements. If so, the RANnode 24 provides an indication to the wireless device 22 that CSI-RStransmissions are present in the subframe (step 1102). For example, theRAN node 24 may schedule the wireless device 22 on the downlink of theLA SCell 18 and provide a corresponding downlink scheduling grant to thewireless device 22. As another example, the RAN node 24 may transmit aDCI message to the wireless device 22 that includes an indication thatCSI-RS transmissions are present in the subframe. Conversely, in someembodiments, if the RAN node 24 determines that the LA SCell 18 cannottransmit in the subframe, the RAN node 24 refrains from providing anindication that CSI-RS transmissions are present in the subframe to thewireless device 22 (step 1104).

As discussed above, FIG. 7 illustrates one example of a cellularcommunications network 10 that includes (for a particular wirelessdevice 22) at least one PCell 14 and at least one SCell 18. FIG. 7 showsa base station 12 (for example a Node B or an eNB) that can be used inexample embodiments described herein. It will be appreciated thatalthough a macro eNB will not in practice be identical in size andstructure to a micro eNB, for the purposes of illustration, the basestations 12 are assumed to include similar components. Further, for thepurposes of illustration, the low power nodes 16 are assumed to includecomponents similar to those of the base stations 12.

As illustrated in FIG. 18, the base station 12 includes a processingmodule 26 that controls the operation of the base station 12. In someembodiments, the processing module 26 includes one or more processors,or processor circuits, 28 (e.g., Central Processing Units (CPUs),Application Specific Integrated Circuits (ASICs), Field ProgrammableGate Arrays (FPGAs), or the like). The processing module 26 is connectedto a transceiver module 30 with associated antenna(s) 32 which are usedto transmit signals to, and receive signals from, wireless devices 22 inthe cellular communications network 10. The transceiver module 30includes one or more transmitters 34 and one or more receivers 36. Thebase station 12 also comprises a memory module 38 that is connected tothe processing module 26 and that stores program and other informationand data required for the operation of the base station 12. The basestation 12 also includes components and/or circuitry for allowing thebase station 12 to exchange information with other base stations 12 (forexample via an X2 interface) and components and/or circuitry forallowing the base station 12 to exchange information with nodes in thecore network 20 (for example via the S1 interface) (e.g., a networkinterface 40). It will be appreciated that base stations 12 for use inother types of networks (e.g., a Universal Terrestrial RAN (UTRAN) or aWideband Code Division Multiple Access (WCDMA) RAN) will includeinterface circuitry for enabling communications with the other networknodes in those types of networks (e.g., other base stations, mobilitymanagement nodes, and/or nodes in the core network 20).

In some embodiments, a computer program including instructions which,when executed by at least one processor, causes the at least oneprocessor to carry out the functionality of the base station 12 (or moregenerally the RAN node 24) according to any one of the embodimentsdescribed herein is provided. In some embodiments, a carrier containingthe aforementioned computer program product is provided. The carrier isone of an electronic signal, an optical signal, a radio signal, or acomputer readable storage medium (e.g., a non-transitory computerreadable medium such as the memory module 38).

FIG. 19 is a block diagram of the base station 12 according to someother embodiments of the present disclosure. This discussion is equallyapplicable to the other RAN nodes 24. As illustrated, the base station12 includes a CSI configuration module 42, a CSI report processingmodule 44, and, in some embodiments, an indication module 46, each ofwhich is implemented in software. Notably, the modules 42 through 46 ofFIG. 19 are implemented in software, whereas the modules 26, 30, and 38of FIG. 18 are implemented, at least partially, in hardware. The CSIconfiguration module 42 operates to configure wireless devices 22 forCSI measurements and reporting, as discussed above. The CSI reportprocessing module 44 operates to, e.g., select downlink transmissionparameters based on the CSI reports received from the wireless devices22. In some embodiments, the indication module 46 operates to send, viaan associated transmitter (not shown), indications to the wirelessdevices 22 of when their associated LA SCells 18 transmit CSI-RSs, asdiscussed above.

FIG. 20 is a block diagram of a wireless device 22 (or UE), according toone exemplary embodiment, that can be used in one or more of thenon-limiting example embodiments described herein. The wireless device22 may in some embodiments be a mobile device that is configured forMachine-to-Machine (M2M) or Machine-Type Communication (MTC). Thewireless device 22 comprises a processing module 48 that controls theoperation of the wireless device 22. In some embodiments, the processingmodule 48 includes one or more processors, or processor circuits, 50(e.g., CPUs, ASICs, FPGAs, or the like). The processing module 48 isconnected to a receiver or transceiver module 52 with associatedantenna(s) 54 which are used to receive signals from or both transmitsignals to and receive signals from a RAN node 24 in the cellularcommunications network 10. The receiver or transceiver module 52includes one or more transmitters 56 (optional) and one or morereceivers 58. To make use of Discontinuous Reception (DRX), theprocessing module 48 can be configured to deactivate the receiver ortransceiver module 52 for specified lengths of time. The wireless device22 also comprises a memory module 60 that is connected to the processingmodule 48 and that stores program and other information and datarequired for the operation of the wireless device 22. In someembodiments, the wireless device 22 may optionally comprise a satellitepositioning system (e.g., Global Positioning System (GPS)) receivermodule that can be used to determine the position and speed of movementof the wireless device 22 (not shown).

In some embodiments, a computer program including instructions which,when executed by at least one processor, causes the at least oneprocessor to carry out the functionality of the wireless device 22according to any one of the embodiments described herein is provided. Insome embodiments, a carrier containing the aforementioned computerprogram product is provided. The carrier is one of an electronic signal,an optical signal, a radio signal, or a computer readable storage medium(e.g., a non-transitory computer readable medium such as the memorymodule 60).

FIG. 21 is a block diagram of the wireless device 22 according to someother embodiments of the present disclosure. As illustrated, thewireless device 22 includes detection module 62, a measurement module64, and a reporting module 66, each of which is implemented in software.Notably, the modules 62 through 66 of FIG. 21 are implemented insoftware, whereas the modules 48, 52, and 60 of FIG. 20 are implemented,at least partially, in hardware. The detection module 62 operates todetect whether CSI-RS transmissions from a LA SCell 18 are present in asubframe, as described above. The measurement module 64 operates toperform CSI-RS and, potentially, CSI-IM measurements as described above.The reporting module 66 operates to generate and send CSI reports to aRAN node 24, as described above.

As disclosed herein, IEEE 802.11 equipment uses a contention basedmedium access scheme. This scheme does not allow the wireless medium tobe reserved at specific instances of time. Instead, IEEE 802.11compliant devices only support the immediate reservation of the wirelessmedium following the transmission of at least one medium reservationmessage (e.g., Request to Transmit (RTS), Clear to Transmit (CTS), orothers). To allow the LA-LTE frame in the SCell to be transmitted atrecurring time intervals that are mandated by the LTE frame in thePCell, in some embodiments, a LA-LTE system that can transmit at leastone of the aforementioned medium reservation messages to blocksurrounding IEEE 802.11 compliant devices from accessing the wirelessmedium.

The present disclosure addresses the above deficiencies by UEimplementation where the UE first detects whether the CSI-RS is presentbefore taking the CSI-RS measurement in the current subframe intoaccount in the CSI processing and reporting. The detection could eitherbe blind by the UE, or guided by explicit signaling from the eNB.

The disclosure has certain advantages that are readily apparent to thoseof skill in the art. For example, one advantage is the avoidance of CSIbuffer corruption, in turn leading to improved quality of CSI estimates.Another advantage is the improvement of the downlink throughput due toincreased link adaptation.

The following acronyms are used throughout this disclosure.

-   -   μs Microsecond    -   3GPP Third Generation Partnership Project    -   AP Access Point    -   ARQ Automatic Repeat Request    -   ASIC Application Specific Integrated Circuit    -   CA Carrier Aggregation    -   CC Component Carrier    -   CFI Control Format Indicator    -   CIF Carrier Indicator Field    -   CPU Central Processing Unit    -   CQI Channel Quality Information    -   CRS Cell Specific Reference Symbol    -   CSI Channel State Information    -   CSI-IM Channel State Information Interference Measurement    -   CSI-RS Channel State Information Reference Symbol    -   CSMA/CA Carrier Sense Multiple Access with Collision Avoidance    -   CTS Clear to Transmit    -   DCI Downlink Control Information    -   DFT Discrete Fourier Transform    -   DRS Dedicated Reference Signal    -   DRX Discontinuous Reception    -   eNB Enhanced or Evolved Node B    -   EPDCCH Enhanced Physical Downlink Control Channel    -   FDD Frequency Division Duplex    -   FPGA Field Programmable Gate Array    -   GHz Gigahertz    -   GPS Global Positioning System    -   LA License Assisted    -   LA-LTE License Assisted Long Term Evolution    -   LAA License Assisted Access    -   LBT Listen-Before-Talk    -   LTE Long Term Evolution    -   M2M Machine-to-Machine    -   MCS Modulation and Coding Scheme    -   MHz Megahertz    -   ms Millisecond    -   MTC Machine-Type Communication    -   NZP Non-Zero Power    -   OFDM Orthogonal Frequency Division Multiplexing    -   PCell Primary Cell    -   PDCCH Physical Downlink Control Channel    -   PDSCH Physical Downlink Shared Channel    -   PMI Precoding Matrix Indicator    -   PSS Primary Synchronization Signal    -   PUCCH Physical Uplink Control Channel    -   PUSCH Physical Uplink Shared Channel    -   RAN Radio Access Network    -   RI Rank Indicator    -   RRC Radio Resource Control    -   RRH Remote Radio Head    -   RTS Request to Transmit    -   SCell Secondary Cell    -   SINR Signal to Interference plus Noise Ratio    -   SSS Secondary Synchronization Signal    -   TS Technical Specification    -   UE User Equipment    -   UTRAN Universal Terrestrial Radio Access Network    -   WCDMA Wideband Code Division Multiple Access    -   WLAN Wireless Local Area Network    -   ZP Zero Power

Those skilled in the art will recognize improvements and modificationsto the embodiments of the present disclosure. All such improvements andmodifications are considered within the scope of the concepts disclosedherein and the claims that follow.

What is claimed is:
 1. A wireless device enabled to operate in acellular communications network according to a carrier aggregationscheme using both a licensed frequency band and an unlicensed frequencyband, comprising: a transceiver; at least one processor; and memorycontaining instructions executable by the at least one processor wherebythe wireless device operates to: determine whether a Channel StateInformation Reference Symbol, CSI-RS, transmission from a LicenseAssisted Secondary Cell, LA SCell, of the wireless device is present ina subframe, the LA SCell being in an unlicensed frequency band; processa CSI-RS measurement for the LA SCell for the subframe upon determiningthat a CSI-RS transmission from the LA SCell is present in the subframe;and refrain from processing a CSI-RS measurement for the LA SCell forthe subframe upon determining that a CSI-RS transmission from the LASCell is not present in the subframe; wherein, in order to determinewhether a CSI-RS transmission from the LA SCell of the wireless deviceis present in the subframe, the wireless device further operates todetermine one of a group consisting of: whether the wireless device hasreceived a downlink scheduling grant for the LA SCell for the subframe,wherein determining that a downlink scheduling grant has been receivedfor the LA SCell for the subframe indicates that a CSI-RS transmissionis present in the subframe; whether the subframe is a discovery subframefor the LA SCell, wherein determining that the subframe is a discoverysubframe for the LA SCell indicates that a CSI-RS transmission ispresent in the subframe; and whether the wireless device has received anuplink grant for the LA SCell for the subframe, wherein determining thatthe wireless device has received an uplink grant for the LA SCell forthe subframe indicates that a CSI-RS transmission is not present in thesubframe.
 2. The wireless device of claim 1 wherein, in order todetermine whether a CSI-RS transmission from the LA SCell of thewireless device is present in the subframe, the wireless device furtheroperates to: determine whether the wireless device has received adownlink scheduling grant for the LA SCell for the subframe, whereindetermining that a downlink scheduling grant has been received for theLA SCell for the subframe indicates that a CSI-RS transmission ispresent in the subframe.
 3. The wireless device of claim 1 wherein, inorder to determine whether a CSI-RS transmission from the LA SCell ofthe wireless device is present in the subframe, the wireless devicefurther operates to: determine whether the subframe is a discoverysubframe for the LA SCell, wherein determining that the subframe is adiscovery subframe for the LA SCell indicates that a CSI-RS transmissionis present in the subframe.
 4. The wireless device of claim 1 wherein,in order to determine whether a CSI-RS transmission from the LA SCell ofthe wireless device is present in the subframe, the wireless devicefurther operates to: determine whether the wireless device has receivedan uplink grant for the LA SCell for the subframe, wherein determiningthat the wireless device has received an uplink grant for the LA SCellfor the subframe indicates that a CSI-RS transmission is not present inthe subframe.
 5. The wireless device of claim 1 wherein, via executionof the instructions by the at least one processor, the wireless devicefurther operates to: upon determining that transmission from the LASCell is present in the subframe, perform a first type of interferencemeasurement on configured Channel State Information InterferenceMeasurement, CSI-IM, resources in the subframe; and otherwise, perform asecond type of interference measurement on the configured CSI-IMresources in the subframe.
 6. The wireless device of claim 5 wherein,via execution of the instructions by the at least one processor, thewireless device further operates to: send a Channel State Information,CSI, report to a network node of the cellular communications networkbased on a latest available CSI-RS measurement for the LA SCell and thefirst type of interference measurement upon determining that atransmission from the LA SCell is present in the subframe; andotherwise, send a CSI report to the network node of the cellularcommunications network based on the latest available CSI-RS measurementfor the LA SCell and the second type of interference measurement.
 7. Thewireless device of claim 5 wherein, via execution of the instructions bythe at least one processor, the wireless device further operates to:determine whether a latest available valid CSI-RS measurement for the LASCell is older than a predefined age threshold; upon determining thatthe latest available valid CSI-RS measurement for the LA SCell is olderthan the predefined age threshold, send an indication to a network nodeof the cellular communications network that the latest available validCSI-RS measurement is older than the predefined age threshold; and upondetermining that the latest available valid CSI-RS measurement for theLA SCell is not older than the predefined age threshold: send a ChannelState Information, CSI, report to the network node of the cellularcommunications network based on the latest available valid CSI-RSmeasurement for the LA SCell and the first type of interferencemeasurement upon determining that the latest available valid CSI-RSmeasurement for the LA SCell is made in the same subframe from which thefirst type of interference measurement; and otherwise, send a CSI reportto the network node of the cellular communications network based on thelatest available valid CSI-RS measurement for the LA SCell and thesecond type of interference measurement.
 8. The wireless device of claim1 wherein, via execution of the instructions by the at least oneprocessor, the wireless device further operates to: send a Channel StateInformation, CSI, report to a network node of the cellularcommunications network.
 9. A method of operation of a wireless deviceenabled to operate in a cellular communications network according to acarrier aggregation scheme using both a licensed frequency band and anunlicensed frequency band, comprising: determining whether a ChannelState Information Reference Symbol, CSI-RS, transmission from a LicenseAssisted Secondary Cell, LA SCell, of the wireless device is present ina subframe, the LA SCell being in an unlicensed frequency band;processing a CSI-RS measurement for the LA SCell for the subframe upondetermining that a CSI-RS transmission from the LA SCell is present inthe subframe; and refraining from processing a CSI-RS measurement forthe LA SCell for the subframe upon determining that a CSI-RStransmission from the LA SCell is not present in subframe; whereindetermining whether a CSI-RS transmission from the LA SCell of thewireless device is present in the subframe comprises one of a groupconsisting of: determining whether the wireless device has received adownlink scheduling grant for the LA SCell for the subframe, whereindetermining that a downlink scheduling grant has been received for theLA SCell for the subframe indicates that a CSI-RS transmission ispresent in the subframe; determining whether the subframe is a discoverysubframe for the LA SCell, wherein determining that the subframe is adiscovery subframe for the LA SCell indicates that a CSI-RS transmissionis present in the subframe; and determining whether the wireless devicehas received an uplink grant for the LA SCell for the subframe, whereindetermining that the wireless device has received an uplink grant forthe LA SCell for the subframe indicates that a CSI-RS transmission isnot present in the subframe.
 10. The method of claim 9 whereindetermining whether a CSI-RS transmission from the LA SCell of thewireless device is present in the subframe comprises: determiningwhether the wireless device has received a downlink scheduling grant forthe LA SCell for the subframe, wherein determining that a downlinkscheduling grant has been received for the LA SCell for the subframeindicates that a CSI-RS transmission is present in the subframe.
 11. Themethod of claim 9 wherein determining whether a CSI-RS transmission fromthe LA SCell of the wireless device is present in the subframecomprises: determining whether the subframe is a discovery subframe forthe LA SCell, wherein determining that the subframe is a discoverysubframe for the LA SCell indicates that a CSI-RS transmission ispresent in the subframe.
 12. The method of claim 9 wherein determiningwhether a CSI-RS transmission from the LA SCell of the wireless deviceis present in the subframe comprises: determining whether the wirelessdevice has received an uplink grant for the LA SCell for the subframe,wherein determining that the wireless device has received an uplinkgrant for the LA SCell for the subframe indicates that a CSI-RStransmission is not present in the subframe.
 13. The method of claim 9further comprising: upon determining that transmission from the LA SCell is present in the subframe, performing a first type of interferencemeasurement on configured Channel State Information InterferenceMeasurement, CSI-IM, resources in the subframe; and otherwise performinga second type of interference measurement on the configured CSI-IMresources in the subframe.
 14. The method of claim 13 furthercomprising: sending a Channel State Information, CSI, report to anetwork node of the cellular communications network based on a latestavailable CSI-RS measurement for the LA SCell and the first type ofinterference measurement upon determining that transmission from the LASCell is present in the subframe; and otherwise, sending a CSI report tothe network node of the cellular communications network based on thelatest available CSI-RS measurement for the LA SCell and the second typeof interference measurement.
 15. The method of claim 13 furthercomprising: determining whether a latest available valid CSI-RSmeasurement for the LA SCell is older than a predefined age threshold;upon determining that the latest available valid CSI-RS measurement forthe LA SCell is older than the predefined age threshold, sending anindication to a network node of the cellular communications network thatthe latest available valid CSI-RS measurement is older than thepredefined age threshold; and upon determining that the latest availablevalid CSI-RS measurement for the LA SCell is not older than thepredefined age threshold: sending a Channel State Information, CSI,report to the network node of the cellular communications network basedon the latest available valid CSI-RS measurement for the LA SCell andthe first type of interference measurement upon determining that thelatest available valid CSI-RS measurement for the LA SCell is made inthe same subframe from which the first type of interference measurement;and otherwise, sending a CSI report to the network node of the cellularcommunications network based on the latest available valid CSI-RSmeasurement for the LA SCell and the second type of interferencemeasurement.
 16. The method of claim 9 further comprising: sending aChannel State Information, CSI, report to a network node of the cellularcommunications network.
 17. A method of operation of a network node,comprising: determining whether an License Assisted Secondary Cell, LASCell, of a wireless device is permitted to transmit in an unlicensedfrequency band in a subframe in which a Channel State InformationReference Symbol, CSI-RS, measurement is configured for the wirelessdevice; and upon determining that the LA SCell of the wireless device ispermitted to transmit in the unlicensed frequency band in the subframein which the CSI-RS measurement is configured for the wireless device,providing an indication to the wireless device that a CSI-RStransmission is present or not present in the subframe, the indicationbeing one from the group of: a downlink scheduling grant for the LASCell, which indicates that a CSI-RS transmission is present in thesubframe; a discovery subframe for the LA SCell, which indicates that aCSI-RS transmission is present in the subframe; and an uplink grant forthe LA SCell, which indicates that a CSI-RS transmission is not presentin the subframe.
 18. The method of claim 17 wherein the indication iscomprised in a Downlink Control Information, DCI, message.
 19. Awireless device enabled to operate in a cellular communications networkaccording to a carrier aggregation scheme using both a licensedfrequency band and an unlicensed frequency band, comprising: atransceiver; at least one processor; and memory containing instructionsexecutable by the at least one processor whereby the wireless deviceoperates to: determine whether a Channel State Information ReferenceSymbol, CSI-RS, transmission from a License Assisted Secondary Cell, LASCell, of the wireless device is present in a subframe, the LA SCellbeing in an unlicensed frequency band; process a CSI-RS measurement forthe LA SCell for the subframe upon determining that a CSI-RStransmission from the LA SCell is present in the subframe; and refrainfrom processing a CSI-RS measurement for the LA SCell for the subframeupon determining that a CSI-RS transmission from the LA SCell is notpresent in the subframe; wherein, in order to determine whether a CSI-RStransmission from the LA SCell of the wireless device is present in thesubframe, the wireless device further operates to determine whether aDownlink Control Information, DCI, message received by the wirelessdevice in a self-scheduling message on the LA SCell includes anindication that a CSI-RS transmission is present in the subframe.